Control system for fluid fuel burners



April 12, 1966 P. D. cox

CONTROL SYSTEM FOR FLUID FUEL BURNERS Filed Jan. 28, 1964 LEE-=- FLAME UNDEF PR s R DETECTOR 5 1 8;

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ATTORNEYS United States Patent 3 245 456 CONTROL SYSTEM FbR lFLUID FUEL BURNERS Paul D. Cox, Ridgeville, Ind., assignor to Cox Manufacturing Company, Ridgeviile, Ind., a partnership Filed Jan. 28, 1964, Ser. No. 340,627 17 Claims. (Cl. 15828) This invention relates generally to burners for fluid fuel, including both gaseous and liquid fuels, and more particularly to a safety control system for fluid fuel burners.

Conventional domestic fuel burners, both gas and oil, comprise a nozzle for introducing the fuel to be burned into a combustion chamber, a blower for supplying combustion air to the combustion chamber, and ignition electrodes positioned adjacent the nozzle for igniting the fuel. In the case of oil burners, the fuel is conventionally supplied to the nozzle under pressure by (a pump commonly driven by the same motor which drives the blower, while in a gas burner the gas, already under pressure, is commonly supplied to the nozzle from the gas supply line by a solenoid-actuated valve; gas burners also commonly include :a pilot nozzle for providing a pilot flame with a pilot valve supplying gas thereto. Both oil and gas burner systems are conventionally actuated in response to a thermostat device.

In the design of fluid fuel burner systems, it is desirable that certain safety features be provided. For example, when the system is initially energized in response to the thermostat or other control sensing a predetermined lower temperature or other condition at which heat is to be supplied, it is desirable that the blower be operated for a period of time prior to the introduction of fuel into the combustion chamber and ignition thereof in order to purge accumulated gases from the combustion chamber which may remain from a previous cycle of operation or which have resulted from a leaking valve or pump; such prepurging is desirable in order to prevent the explosion of such accumulated gases. Following prepurging of the combustion chamber and introduction and ignition of the fuel therein, it is desirable to determine whether or not the flame has actually been established in the combustion chamber and if not, to terminate fuel flow and ignition; if for some reason the blower has not started so that prepurging has not been accomplished, it is further desirable that introduction and ignition of the fuel in the combustion chamber be prevented. Further, if prepurging has been accomplished but the flame has not been established and introduction of fuel and ignition thereof in the combustion chamber terminated, it is desirable that the blower continue to operate in order to provide a post-purging of the gases in the chamber which were not ignited. In the case of a gas burner, it is desirable that the main gas valve be actuated only if the pilot flame has been established and that the main gas valve be prevented from opening, or be closed if already open, as the case may be, if the gas pressure falls below a predetermined level. Safety control devices for variously accomplishing the foregoing functions have been provided; however, to the best of the present applicants knowledge, such devices have either failed to provide all of the desirable safety features, or have been characterized by their complexity and relatively high cost. It is desirable, therefore, to provide the safety control system for a fluid fuel burner which will accomplish all of the foregoing safety objectives with the employment of simple circuitry utilizing a minimum number of inexpensive, commercially available components.

It is accordingly an object of the invention to provide an improved fluid fuel burner control system.

. Another object of my invention is to provide an im- 3,245,456 Patented Apr. 12, 1966 'ice proved safety control system for fluid fuel burners in which prepurging, flame sensing and post-purging are provided.

A further object of my invention is to provide an improved safety control system for a fluid fuel burner which performs all of the requisite safety functions with a circuit which is more simple and employs fewer component devices than the systems heretofore have provided for performing the same functions.

Further objects and advantages of my invention will become apparent by reference to the following description and the accompanying drawings, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

The invention in its broader aspects provides a fluid fuel burner control system incorporating fluid nozzle means for introducing the fluid to be burned into a combustion chamber and electrically actuated valve means for connecting the nozzle means to a fluid fuel supply line. Electrically energized ignition means are provided [for igniting the fluid in the combustion chamber and electrically energized blower means are provided for supplying combustion air to the combustion chamber. First means are provided for selectively energizing the blower means, as when the thermostat calls for heat. Second means are provided for energizing the valve means and ignition means a first predetermined time after energization of the blower means so that the blower means prepurges the chamber during the first time prior to introduction and ignition of fluid therein. Means are provided for detecting the presence of flame in the combustion chamber and for disabling the second energizing means -a second predetermined time after the first predetermined time in response to the detecting means failing to detect flame thereby to de-energize the valve means and ignition means, the blower means continuing to operate following such de-energization to post-purge the combustion chamber.

In the drawings:

FIG. 1 is a schematic illustration of the fluid fuel burner control system of the invention incorporated in a gas burner; and

FIG. 2 is a fragmentary schematic illustration of a modification of the system of FIG. 1 employing a different form of blower operation sensing switch.

Referring now to FIG. 1, there is shown a gas burner system, generally indicated at 10 having a gas supply line 12 adapted to be connected to a source of gas under pressure which may be either natural or mixed gas from a gas line, or low pressure gas from a supply tank. A main gas nozzle 14 is provided positioned in the combustion chamber of the-furnace or heater (not shown) in conventional fashion, the main nozzle 14 being connected to the gas supply line 12 by suitable piping '16 and a conventional solenoid operated main gas valve 18 having an operating coil 20. A conventional pilot nozzle 22 is also provided positioned adjacent the main nozzle 14 in the combustion chamber in conventional fashion and connected to the gas or oil line 12 by suitable piping 24, 26 and a conventional pilot gas valve 28 having an operating coil 30.

A blower 32 is provided for supplying combustion and purging air to the combustion chamber, the blower 32 comprising an operating motor 34 and a conventional impeller shown schematically at 37. In the illustrated embodiment, in which the source of energizing potential for the system 10 is single phase, alternating current, such as volts, 60 cycles, blower motor 34 is of the split phase, capacitor-start variety, having starting and running field windings 36, 38, each having one end connected ,to

terminal 40. Starting capacitor 42 is connected in series with the other end of the starting winding 36. The other end of the running winding 38 is connected to another terminal 44 and a conventional centrifugally-actuated starting switch 46 is provided having its moving element '48 connecting terminal 44 to starting contact 50 when the motor is at rest. Thus, when the motor is at rest and below a predetermined running speed, movable element 48 of starting switch 46 connects the serially coupled starting winding 36 and starting capacitor 42 in parallel with the running winding 38, as is well known to those skilled in the art. When a predetermined motor operating speed is reached, movable element 48 of the starting switch 46 moves away from its starting contact 50 to engage running or back contact 52 which is connected to a terminal 54. It will be readily understood that other conventional split-phase motor configurations may be employed provided a starting switch having back contacts is employed.

Line terminals 56, '58 are provided for connection to a suitable source of single phase alternating current, as by means of a suitable line switch 60. A conventional room thermostat may be provided, shown schematically at 62, which in its simplest form comprises a bimetallic mechanism 64 arranged to close switch contacts 66 "in response to the ambient temperature falling to a predetermined 'lowerlevel, and to opencontacts66-in response to the temperature rising to a predetermined upper level. -In accordance with conventional practice, contacts 66 of room thermostat 62 are coupled in a low voltage circuit and thus a step-down transformer 68 is provided having its primary winding 70 coupled across alternating current supply line 59 and having a low voltage secondary winding 72. A low voltage relay 74 is accordingly provided having an operating coil 76 coupled to terminals '78, '80. Low voltage secondary winding 72 of trans- :former 68 and room thermostat contacts 66 are serially coupled across terminals 78, 80 and thus across operating coil 76 of relay 74. Relay 74 is provided with normally open contacts '82 which are closed in response to energization of operating coil 76. Line terminal '58 isdirectly coupled to motor terminal'44 by a conductor 84 and line terminal 56 is connected to motor terminal "40 by conductor 86, normally open relay contacts .82 and conductor 88. It will now be seen that when the ambient temperature sensed by the room thermostat falls below the predetermined lower level, contacts 66 will be closed thus energizing operating coil 76 of relay 74 from secondary winding 72 of transformer 68. Relay contacts 82 will thus pick up coupling blower motor 34 directly across line 54 for energization therefrom. It will be readily understood that a control device other than a thermostat may be employed, such as an aquastat in the case of a liquid heating system, or any other device for sensing a condition at which heat is to be supplied. It will also be understood that the low voltage relay 74 may be eliminated with contacts 66 of sensing device 64 then coupled in series-in line 86, 88 replacing relay contacts 82.

With motor 34 energized as above-described in response to the room thermostat 62 calling for heat, if the motor starts and comes up to operating speed properly, movable element 48 of starting switch 46 will be moved from its starting contact 50 to its back or running contact 52 and the motor 34 will thus operate impeller 37 so as to purge accumulated gases from the combustion chamber, as above described.

Conventional ignition electrodes 90 are provided adjacent main and pilot nozzles 14, 22, electrodes 90 being coupled across secondary winding 92 of a conventional high voltage ignition transformer 94 having a primary winding 96.

In order to provide for energizat-ion of operating coil 3t? of the pilot gas valve 28 and primary winding 96 of ignition transformer $4 after a predetermined period during which the blower motor 34 is operated so as to purge accumulated gases from the combustion chamber, and further to energize operating coil 30 of pilot gas valve 28 and primary winding 96 of ignition transformer 4 only if the blower motor 34 was successfully started, to de-energize operating coil 30 and primary winding 96 if flame is not established, and to energize operating coil 28 of main gas valve 18 only if flame is established and adequate gas pressure is provided, the arrangement now to be described is provided. A first thermal time delay relay 98 is provided having a heater 100 coupled for energization across the energizing circuit for the blower motor 34 which comprises conductors 84, 88. Thermal relay 98 has normally open thermally-actuated contacts 102 which are closed after a predetermined time delay in response to heating by the heater 100. A second thermal relay 104 is provided having a heater 106 and normally closed thermally-actuated contacts 108 which are opened after a predetermined time delay in response to heating by the heater "106. Heater 1060f thermal time delay relay 104 is coupled across conductors 84, 88 by normally open contacts 102 of thermal time delay relay 98. Normally open contacts 102 of thermal time delay relay 98 and normally closed contacts 108 of thermal time delay relay 16M serially couple conductor 88 to terminal 116 to 'which one side of primary winding 96 of ignition transformer 98 and one side of operating coil '30 or pilot gas valve 28 are connected, the other sides of primary winding 96 and operating coil 30 being connected to terminal '54 to which the back contacts 52 of motor starting switch 46 are connected; it will be observed that operating coil 30 of pilot gas valve 28 and primary winding 96 of ignition transformer are connected in parallel across terminals 54, 110.

A third thermal time delay relay '112 is provided 'having a heater 1'14 and normally open thermally-actuated contacts 116. Normally open contacts 116 of thermal time delay relay 112 are connected across-normally'closed contacts 108 of thermal time delay relay 104, as shown.

One end of heater 114 of thermal time delay relay 112 is connected to conductor 84 and the other end is connee-ted to a-terminal 118.

A conventional flame detector device is provided "for detecting or sensing the presence of flame in the combustionchambcr and having normally open contacts 122 which are closed in response to the detection of flame. Contacts 122 are connected across terminals 40, 118 and thus when closed serially connect heater 114 of thermal time delay relay 112 across conductors 84, 88. A conventional gas pressure switch 124 may also be provided suitably connected to the gas supply line 12 and having normally closed contacts 126 which are opened in response to the gas pressure falling below a predetermined lower level. Contacts 126 serially couple operating coil 20 of main gas valve 18 across terminals 54, 118.

Time delay relay 112 has a time delay for closing of its normally open contacts 116 shorter, and preferably substantially shorter than the time delay provided by thermal time delay relay 164 for the opening of its normally closed contacts 108. In an actual embodiment of the system of FIG. 1, thermal time delay relay 98 is a catalog number 115NO4ST relay manufactured by Amprite Company and having a 4S-second time delay relay for closing of its contacts 102, thermal time delay relay 104 is a catalog number 115C45T relay manufactured by Amprite Company and having a 45-second time delay for opening of its contacts 108 and thermal time delay relay 112 is a catalog number 1l5NO3T relay manufactured by Amprite Company and having a 3-sec- 0nd time delay for closing of its contacts 116. it will be readily understood that there are many commercially available forms of thermal time delay relays which may be employed for relays 98, 104, and 112; I consider it desirable that thermal time delay relay 98 have a time delay for closing of its contacts 16.2 between 45 seconds and seconds, that thermal time delay relay 1424 have a time delay for opening of its contacts 108 on the order of 45 seconds, and that the time delay for closing of contacts 116 of thermal time delay relay 112 be as short as possible.

Assuming now that the room thermostat 62 has called for heat and that blower motor 34 has thus been energized as above described, heater 100 of thermal time delay relay 98 will be energized and after its time delay, i.e., 45 seconds in the specific embodiment, its contacts 102 will be closed. Assuming further that the blower motor 34 has satisfactorily started and come up to operating speed, movable element 48 of starting switch 46 will move from its starting contacts 50 to its back contacts 52 and it will now be seen that the blower motor 34 will operate the impeller 36 so as to prepurge accumulated gases from the combustion chamber during the 45 second interval prior to closing of contacts 102 of thermal time delay relay 98. When the contacts 192 are closed and assuming that the blower motor 34 has star-ted as aforesaid, it will be seen that a circuit is established from conductor 88 through the now-closed contacts 102, the still closed contacts 108 of thermal time delay relay 194, primary winding 96 of ignition transformer 94 and operating coil 38 of pilot gas valve 28, and movable element 48 of starting switch 46 engaging its back contacts 52 to conductor 84 thus energizing operating coil 38 to open the pilot gas valve 28 and energizing ignition transformer 94 thereby to energize ignition electrodes 99 so as to ignite the gas introduced into the combustion chamber by the pilot nozzle 22. It will be observed, however, that if the blower motor 34 had failed to start and to come up to operating speed, movable element 48 of startingstarting switch 46 would not have moved to engage back contacts 52 and thus the energizing circuit for operating coil 30 of pilot gas valve 28 and primary winding 96 of ignition transformer 94 would not have been established despite closing of contacts 102 of thermal time delay relay 98 in response to energization of heater 100.

Closing of contacts 102 of thermal time delay relay 98 as above-described couples heater 1136 of thermal time delay relay 194 across conductors 84, 88 for energization and thus after the predetermined time delay, i.e., 45 seconds in the specific embodiment, contacts 188 will be opened so as to break the energizing circuit for the operating coil 30 of pilot gas valve 28 and primary Winding 96 of ignition transformer 94 thus to de-energize operating coil 30 and primary winding 96 unless flame has been established in the combustion chamber as will now be described.

Assuming that flame has been established in the combustion chamber at the pilot nozzle 22, flame detector 120 will actuate contacts 122 thus to energize heater 114 of thermal time delay relay 112. Contacts 116 will therefore be closed after a short time delay, i.e., 3 seconds in the specific embodiment, thereby short-circuiting the contacts 108 of thermal time delay relay 104. Thus, with flame established, operating coil 30 of pilot gas valve 28 and primary winding 96 of ignition transformer 94 will remain energized through contacts 116 of thermal time delay relay 112 despite opening of contacts 108 of ther' mal time delay relay 104 after its time delay, i.e., 45 seconds in the specific embodiment.

With flame having been established in the combustion chamber as above-described, thus causing flame detector 120 to close its contacts 122, and assuming that adequate gas pressure is provided so that contact 126 of the gas pressure switch 124 remains closed, operating coil 20 of the main gas valve 18 will be energized thereby to open the main gas valve and to supply gas to the main nozzle 14. The system will then continue to operate with gas being supplied to both the main and pilot nozzles 14, 22 by the actuated main and pilot gas valves 18, 28

and with continuous ignition provided by ignition transformer 94 until room thermostat 62 opens contacts 66.

Opening of contacts 66 in response to satisfaction of the heat demand will result in de-energization of operating coil 76 of low voltage relay 74 which will in turn drop out its contacts 82 immediately to de-energize blower motor 34. De-energization of motor 34 will in turn result in movement of movable element 48 of starting switch 46 back to its starting position 50 as the motor slows down. Furthermore, opening of contacts 82 will remove the alternating current energizing potential applied by line 59 to conductors 84, 88 thus immediately de-energizing operating coil 20 of main gas valve 18, operating coil 30 of pilot gas valve 28 and primary winding 96 of ignition transformer 94. Thus, the entire system is immediately de-energized and shut-down in response to opening of the room thermostat contacts 66.

Assuming now that flame is not established following energization of operating coil 30 of pilot gas valve 28 and energization of primary winding 96 of ignition transformer 94, it will be seen that contacts 122 of the flame detector 129 will not be closed and thus that the heater 114 of thermal time delay relay 112 will not be energized. Thus, contacts 116 of thermal time delay relay 112 will not be closed and after the predetermined time delay of thermal .time delay relay 194, i.e., 45 seconds in the specific embodiment, contacts 108 will open thus breaking the energizing circuit of operating coil 30 of pilot gas valve 28 and primary winding 26 of ignition transformer 94 thus to close the pilot gas valve 28 and to terminate the energization of the ignition electrodes 90. However, it will be observed that the room thermostat 62 will still be calling for heat and thus its contacts 66 will still be closed so that contacts 82 of relay 76 will in turn still be closed so that the blower motor 34 will continue to operate to provide post-purging of the gases in the combustion chamber which were admitted by the pilot gas valve 28 during the 45 second period (the time delay on drop out of thermal time delay relay 104) during which operating coil 30 was energized.

Turning now briefly to FIG. 2, an arrangement is shown in which the blower motor 34 is provided with a conventional single pole starting switch 128, i.e.,not being provided with the back contacts 52 of the starting switch 4660f 'FIG. 1. In this embodiment in order to prevent energization of the main and pilot gas valves 18, 28 and the ignition transformer 94 in the event that the motor 34 does not start and satisfactorily come up to operating speed, a conventional air movement-responsive or sail switch is provided having normally open contacts 130 connected between motor terminal 44 and terminal 54. Switch'128 is in the air stream provided by impeller 37 and thus when the motor 34 starts and a predetermined velocity of air flow is provided by impeller 37, contacts 130 will be closed .to provide the same function as the movement of element 48 of starting switch 46 to back contacts 52 in the embodiment of FIG. 1. It will be readily understood that other conventional devices for sensing operation of motor 34 and impeller 37 may be provided.

It will be readily seen that in a gas burner system which does not incorporate a pilot nozzle, the main gas valve 18 and its operating coil 20 of the embodiment of FIG. 1 will be eliminated, the valve 28 and nozzle 22 then serving as the main .gas valve :and nozzle. In such an arrangement, contacts 126 of the gas pressure switch 124 may be connected in series with operating coil 30 of valve 28. It will further be seen that the system of FIG. 1 is equally applicable to a conventional domestic oil burner. In that case, again the main valve 18 would be eliminated and the conventional pump, typically driven by motor 34, would be coupled to supply oil under pressure to the valve 28.-

It will now be seen that all of the system components shown outside of the dashed line box 132 in FIG. 1 are provided in a conventional burner system and that the improved safety control of the invention is provided by the connection and arrangement of the three thermal time delay relays 93, 104, and 112 as above described. It will thus be seen that the improved burner control system of the invention provides all of the requisite safety functions with a minimum number of inexpensive, commercially available components coupled in a circuit characterized by its extreme simplicity.

While I have illustrated and described a specific embodiment of my invention, further modifications and improvements will occur to those skilled in the art and I desire therefore in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What is claimed is:

1. A fluid fuel burner control system comprising: fluid nozzle means for introducing fluid to be burned into a combustion chamber; electrically actuated valve means for connecting said nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; electrically energized blower means for supplying combustion air to said chamber; first means for selectively energizing said blower means; second means for energizing said valve means and said ignition means a first predetermined time after energization of said blower means whereby said blower, means prepurges said chamber for said first time prior to introduction and ignition of fluid therein; means for disabling said second energizing means a second predetermined time after said first predetermined time in response to said detecting means thereby to de-energize said valve means and ignition means whereby said blower means post-purges said chamber following said de-energiziation; and means for detecting the presence of flame in said chamber and including means for overriding said disabling means whereby said valve means and ignition means re main energized after said second time only if flame is established in said chamber.

2. A fluid fuel burner control system comprising: fluid nozzle means for introducing fluid to be burned into a combustion chamber; electrically actuated valve means for connecting said nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; electrically energized blower means for supplying combustion air to said chamber; first circuit means for selectively energizing said blower means; second circuit means coupling said first circuit means to said valve means and said ignition means for energizing the same a first predetermined time after energization of said blower means whereby said blower means prepurges said chamber for said first time prior to introduction and ignition of fluid therein; means for opening said second circuit means a second predetermined time after said first predetermined time in response to sald detecting means thereby to tie-energize said valve means and ignition means whereby said blower means postpurges said chamber following said de-energization; and means for detecting the presence of flame in said chamber and including means for overriding said opening means whereby said valve means and ignition means remain energized after said second time only if flame is established in said chamber.

3. A fluid fuel burner control system comprising: fluid nozzle means for introducing fluid to be burned into a combustion chamber; electrically actuated valve means for connecting said nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; electrically energized blower means for supplying combustion air to said chamber; first circuit means for selectively energizing said blower means; second circuit means coupling said first circuit means to said Valve means and said ignition means for energizing the same a first predetermined time after energization of said blower means whereby said blower means prepurge said chamber for said first time prior to introduction and ignition of fluid therein; said second circuit means including means for opening the same a second predetermined time after said first predetermined time thereby to deenergize said valve means and ignition means whereby said blower means post-purges said chamber following said de-energization; means for detecting the pressure of flame in said chamber; and means for disabling said opening means in response to said detecting means whereby said valve means and ignition means remain energized after said second time only if flame is established in said chamber.

4. A fluid fuel burner control system comprising: fluid nozzle means for introducing fluid to be burned into a combustion chamber; electrically actuated valve means for connecting said nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; electrically energized blower means for supplying combustion air to said chamber; first circuit means for selectively energizing said blower means; second circuit means coupled to said valve means and ignition means for energizing the same; first time delay relay means for coupling said first circuit means to said second circuit means thereby to energize the same a first predetermined time after energization of said blower means whereby said blower means prepurges said chamber prior to introduction and ignition of fluid therein; said second circuit means including second time delay relay means for opening said second circuit means a second predetermined time after energization thereof thereby to deenergize said valve means and said ignition means whereby said blower means post-purges said chamber following said de-energization; means for detecting the presence of flame in said chamber; and means for disabling said second time delay means in response to said detecting means whereby said valve means and ignition means remain energized after said second time only if flame is established in said chamber.

5. The system of claim 4 wherein said disabling means comprises third time delay relay means coupled to said detecting means and energized thereby and having a time delay substantially shorter than said second time.

6. A fluid fuel burner control system comprising: fluid nozzle means for introducing fluid to be burned into a combustion chamber; electrically actuated valve means for connecting said nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; an electric motor adapted to drive a blower for supplying combustion air to said chamber; first circuit means for selectively coupling said motor to a source of energizing potential; second circuit means; first time delay means for coupling said first circuit means to said second circuit means for energizing the same a first predetermined time after energization of said motor whereby said motor operates said blower to prepurge said chamber during said first time; switch means actuated in response to operation of said motor and coupling said second circuit means to said valve means and said ignition means whereby the same are energized by said second circuit means only if said motor is operating; said second circuit including second time delay means for opening said second circuit means a second predetermined time following energization thereof thereby to de-energize said valve means and ignition means whereby said motor operates said blower to post-purge said chamber following said de-energization; means for detecting the presence of flame in said chamber; and means for disabling said second time delay means in response to said detecting means whereby said valve means and ignition means remain energized after said second time only if flame is established in said chamber.

7. The system of claim 6 wherein said switch means comprises an air movement-responsive switch adapted for actuation by said blower.

8. The system of claim 6 wherein said switch means comprises a rotation responsive switch actuated by said motor.

9. The system of claim 6 wherein said source is single phase alternating current, wherein said motor has a splitphase field, said switch means comprising a rotationresponsive switch on said motor coupled with said field and having starting and running positions, said switch in said running position thereof coupling said second circuit means to said valve means and ignition means.

a 10. A fluid fuel burner control system comprising: fluid nozzle means for introducing fluid to be burned into a combustion chamber; electrically actuated valve means for connecting said nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; an electric motor adapted to drive a blower for supplying combustion air to said chamber; a first circuit for selectively coupling said motor to a source of energizing potential; a first thermal time delay relay having a first heater coupled across said first circuit and energized thereby and having first normally open contacts, said first contacts being closed in response to energization of said first heater a first predetermined time after energization of said first circuit and said motor; a second time delay relay having a second heater coupled in series with said first contacts across said first circuit and having second-normally closed contacts, said second contacts being opened in response toenergization of said second heater a second predetermined time after said first predetermined time; switch means actuated to 'a' closed position inres'ponse to operation of said motor; said first and second contacts and said switch means coupling said valve means and said ignition means across said first circuit; flame detector means having third contacts which are closed in response to the presence of flame in said chamber; and a third thermal time delay relay having a third heater serially coupled with said third contacts across said first circuit and having fourth normally open contacts coupled across said second contacts, said fourth contacts being closed in response to energization of said third heater a third predetermined time after closure of said third contacts thereby to maintain energization of said valve means and said ignition means despite opening of said second contacts, said third time delay being substantially shorter than said second time delay.

11. A fluid fuel burner control system comprising: main fluid nozzle means for introducing fluid to be burned into a combustion chamber; pilot fluid nozzle means adjacent said main fluid nozzle means; main and pilot electrically actuated valve means for respectively connecting said main and pilot nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; electrically energized blower means for supplying combustion air to said chamber; first means for selectively energizing said blower means; second means for energizing said pilot valve means and said ignition means a first predetermined time after energization of said blower means whereby said blower means prepurges said chamber for said first time prior to introduction and ignition of fluid therein; means for disabling said second energizing means a second predetermined time after said first time thereby de-energizing said pilot valve means and said ignition means whereby said blower means post-purges said chamber following said tie-energization; means for detecting the presence of flame in said chamber; means for overriding said disabling means in response to said detecting means whereby said pilot valve means and ignition means remain energized after said second time only if flame is established in said chamber; and means for energizing said main valve means in response to said detecting means.

12. A fluid fuel burner control system comprising: main fluid nozzle means for introducing fluid to be burned into a combustion chamber; pilot fluid nozzle means adjacent said main fluid nozzle means; main and pilot electrically actuated valve means for respectively connecting said main and pilot nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; electrically energized blower means for supplying combustion air to said chamber; first circuit means for selectively energizing said blower means; second circuit means coupling said first circuit means to said pilot valve means and said ignition means for energizing the same a first predetermined time after energization of said blower means whereby said blower means prepurges said chamber for said first time prior to introduction and ignition therein; said second circuit means including means responsive to operation of said blower means for energizing said pilot valve means and ignition means only when said blower means is operating; said second circuit means further including means for opening the same a second predetermined time after said first predetermined time thereby to de-energize said pilot valve means and ignition means whereby said blower means postpurges said chamber following said de-energization; means for detecting the presence of flame in said chamber; means for disabling said opening means in response to said detecting means whereby said pilot valve means and ignition means remain energized after said second time only when flame is established in said chamber; and third circuit means for energizing said main valve in response to said detecting means, said third circuit means including said blower operation responsive means.

i 13. Thersystem of claim 12 further comprising means in said third circuit for opening the same thereby to deenergize said main gas valve in response to fluid pressure in said pilot nozzle means below a predetermined level.

14. A fluid fuel burner control system comprising: main fluid nozzle means for introducing fluid to be burned into a combustion chamber; pilot fluid nozzle means adjacent said main fluid nozzle means; main and pilot electrically actuated valve means for respectively connecting said main and pilot nozzle means to a fluid fuel supply line; electrically energized ignition means for igniting said fluid in said chamber; an electric motor adapted to drive a blower for supplying combustion air to said chamber; a first circuit for selectively coupling said motor to a source of energizing potential; a first thermal time delay relay having a first heater coupled across said first circuit and energized thereby and having first normally open contacts, said first contacts being closed in response to energization of said first heater a first predetermined time after energization of said first circuit and said motor; a second time delay relay having a second heater coupled in series with said first contacts across said first circuit and having second normally closed contacts, said second contacts being opened in response to energization of said second heater a second predetermined time after said first predetermined time; switch means actuated to a closed position in response to operation of said motor; said first and second contacts and said switch means coupling said pilot valve means and said ignition means across said first circuit; flame detector means having third contacts which are closed in response to the presence of flame in said chamber; and a third thermal time delayrelay having a third heater serially coupled with said third contacts across said first circuit and having fourth normally open contacts coupled across said second contacts, said fourth contacts being closed in response to energization of said third heater'a third predetermined time after closure of said third contacts thereby to maintain energization of said pilot valve means and said ignition means despite opening of said second contacts, said third time delay being substantially shorter than said second time delay; said switch means and said third contacts serially coupling said main valve means across said first circuit.

15. The system of claim 14 further comprising fluid pressure sensing means having fifth contacts which are opened in response to fluid pressure in said pilot nozzle 1 1 means being below a predetermined level, said fifth contacts being coupled in series with said main valve, means.

16. A safety control system for a fluid fuel burner having electrically energized blower means, electrically actuated fluid valve means, and flame detector means, said control system comprising: first energizing circuit means for connection to said blower, means; means, for selectively couplinglsaid first circuit means to a source of energizing potential; second energizing circuit means for connection to said valve means; first time delay means, for coupling said second circuit means to said. first circuit means after a first predeterminedtime following energization of said first circuit means; second time delay means for opening said second circuit means after a second predetermined time following energizationthereof; and means for overriding said second time delay means, in response to said flame detector means.

17. A safety control system fora fluid fuel burner having electrically actuated blower means, electrically actuated fluid valve means; and flame detector means; and control system comprising: a first energizing circuit l1av ing output terminal means for connection to said blower means; a first relay having first contacts for connecting said first circuit to asource of energizing potential; said first relay means including an operating coil having input terminal means for connection to control means whereby said first circuit is energized when said control means calls for heat; a second energizing circuit having output. terminal means for connection to said valve 12 means; a first terminal relay having a first heater coupled for energization across-.saidfirst circuit anclhaving second normally open contacts, said second contacts being closed in response to energization of said first heater a first predetermined time after energization of said first circuit; a second time delay having a second heater coupled in series with said second contacts across'said: first circuit and having. third normally closed contacts, said third. contacts being openedv inv respose to energization of said second heater a second predetermined time after said first predetermined. time; said? second and: third contacts serially coupling said second circuit to said first circuit; and a third time delay relay having a third heater and fourth normally'open contacts-, said third heater having terminal means for coupling the same in series with said fiame detector across said first circuit whereby said third heater is energized in response to detection of flame by said flame detector, said fourth contacts being: coupled across said third contacts and being closed responsive-to termined time substantially shorter. than said second: time;

References Cited by the Examiner UNITED STATES PATENTS 2,210,852 8/ 1940 Falkenberg 15 828 2,3 8 8,124 1071945 Crews 158 28 2,839,129 6/19533 St. Clair 158 28" JAMES W. \VESTHAVER, Primary Examiner. 

1. A FLUID FUEL BURNER CONTROL SYSTEM COMPRISING: FLUID NOZZLE MEANS FOR INTRODUCING FLUID TO BE BURNED INTO A COMBUSTION CHAMBER; ELECTRICALLY ACTUATED VALVE MEANS FOR CONNECTING SAID NOZZLE MEANS TO A FLUID FUEL SUPPLY LINE; ELECTRICALLY ENERGIZED IGNITION MEANS FOR IGNITING SAID FLUID IN SAID CHAMBER; ELECTRICALLY ENERGIZED BLOWER MEANS FOR SUPPLYING COMBUSTION AIR TO SAID CHAMBER; FIRST MEANS FOR SELECTIVELY ENERGIZING SAID BLOWER MEANS; SECOND MEANS FOR ENERGIZING SAID VALVE MEANS AND SAID IGNITION MEANS A FIRST PREDETERMINED TIME AFTER ENERGIZATION OF SAID BLOWER MEANS WHEREBY SAID BLOWER MEANS PREPURGES SAID CHAMBER FOR SAID FIRST TIME PRIOR TO INTRODUCTION AND IGNITION OF FLUID THEREIN; MEANS FOR DISABLING SAID SECOND ENERGIZING MEANS A SECOND PREDETERMINED TIME AFTER SAID FIRST PREDETERMINED TIME IN RESPONSE TO SAID DETECTING MEANS THEREBY TO DE-ENERGIZE SAID VALVE MEANS AND IGNITION MEANS WHEREBY SAID BLOWER MEANS POST-PURGES SAID CHAMBER FOLLOWING SAID DE-ENERGIZATION; AND MEANS FOR DETECTING THE PRESENCE OF FLAME IN SAID CHAMBER AND INCLUDING MEANS FOR OVERRIDING SAID DISABLING MEANS WHEREBY SAID VALVE MEANS AND IGNITION MEANS REMAIN ENERGIZED AFTER SAID SECOND TIME ONLY IF FLAME IS ESTABLISHED IN SAID CHAMBER. 